Tejada Charged With Lying

Just a quick post to drop in a link to the story by Dave and reporter Del Quentin Wilbur, who are reporting that former Oriole turned Astros shortstop Miguel Tejada has been charged with lying to congressional investigators about the use of performance-enhancing drugs, connected not with his own use, but with "giving false statements to congressional staffers about his conversations with another player about steroids and human growth hormone," all connected with his former Oakland teammate, Adam Piatt.

So how do you convict someone of lying about not having a conversation with another person unless the other person has proof of a conversation? Was Piatt wearing a wire? Were there other witnesses of the conversation? Did Tejada spontaneously confess to previous lies?